In industrial installations, in particular machines and machine systems, a large number of electrical low-voltage loads have to be supplied with electric power. The loads are often, but not exclusively, single-phase or three-phase AC voltage motors. It is also known, for example, for them to be supplied with 500 V DC voltage.
The energy distribution to the loads previously took place in switch cabinets, in which the feeding module for the loads was also arranged. Proceeding from the switch cabinet, separate lines were led to the individual loads. The topology of the line system was consequently star-like. On account of this topology, that is a separate line per load, the dimensioning of the line was relatively easy. It could even be performed by electrical installation engineers on the basis of comparatively simple tables.
Recently, it has become increasingly common for the electrical loads to be connected to the feeding module by means of bus- or network-like line systems. Consequently, from the feeding module there extends a trunk section of the line system, via which a network—which is even possibly made to branch further—is led to the individual loads. The trunk section carries the total current of the connected loads. Further sections branch away to the individual loads, referred to hereafter as individual or end sections, which carry the current for only this one load.
Dimensioning and testing a line system of this type is considerably more complex and expensive than in the case of a star-like topology. It is too much to expect electrical installation engineers to carry this out. Although electrical engineers have in principle the required technical know-how, there are no standardized, easily manageable and readily applicable dimensioning rules. Consequently, even for electrical engineers, proper dimensioning and testing of the dimensioning is possible only by spending considerable time.
It is admittedly conceivable simply to add together the individual lengths of the sections and the rated outputs of the loads and dimension the line system in a standard manner as though it were required for a single load with the total of the rated outputs to be supplied with electric power via a line with the total of the individual lengths of the sections. Although in this case the dimensioning would be easy, it is highly probable that the line system as such would be significantly overdimensioned.